1. Field of the Invention
The present invention relates to Web servers, i.e., server software for delivering content through the World Wide Web.
2. State of the Art
The Internet, and in particular the content-rich World Wide Web (xe2x80x9cthe Webxe2x80x9d), have experienced and continue to experience explosive growth. The Web is an Internet service that organizes information using hypermedia. Each document can contain embedded reference to images, audio, or other documents. A user browses for information by following references. Web documents are specified in HyperText Markup Language (HTML), a computer language used to specify the contents and format of a hypermedia document (e.g., a homepage). HyperText Transfer Protocol (HTTP) is the protocol used to access a Web document.
Web servers offer Web services to Web clients, namely Web browsers. Primarily, Web servers retrieve Web documents and send them to a Web browser, which displays Web documents and provides for user interaction with those documents. Unlike Web browsers, of which there are many, the number of commercially available Web server packages, although growing, remains small. Currently, popular Web servers include those available from Netscape Communications, National Center for Supercomputing Applications (NCSA), and CERN.
Ideally, a Web server should be able to respond to and expeditiously service every connection request it receives, regardless of the volume of requests. The job of getting the request to the server and the reply back to the requester falls to the telecommunications infrastructure. In reality, however, because of machine limitations, there is a limit to the number of requests the server can serve within a given period of time without slowing down the machine to an extent that, from the viewpoint of the users, is perceptible, irritating, or simply intolerable. Web servers have typically followed one of two extreme approaches, either xe2x80x9crationing servicexe2x80x9d by denying further requests once some limiting number of requests are already pending, or attempting to service all requests received and hence slowing the machine to a crawl during extremely busy periods.
Webs servers, most of which are written for UNIX, often run under INETD (xe2x80x9ceye-net-Dxe2x80x9d), an Internet services daemon in UNIX. (A daemon is a UNIX process that remains memory resident and causes specified actions to be taken upon the occurrence of specified events.) Typically, if more than sixty connection requests occur within a minute, INETD will shut down service for a period of time, usually five minutes, during which service remains entirely unavailable. Such interruptions are clearly undesirable, both on the part of the client-requester and the content provider. In the case of other Web servers, when the server is brought up, some fixed number of copies of the server, e.g. 50, are started. Up to 50 simultaneous connections may therefore be handled. A request for a 51st connection, however, will be denied, even if many or all of the 50 existing connections are temporarily idle.
Other considerations further complicate the picture of what is desired from a Web server, including considerations such as cost, perception and the very dynamic nature of the Web and Web content. Typically, only large organizations, or smaller organizations having considerable technical expertise, have their own Web servers. Establishing and running a Web server can entail a significant and ongoing investment in time and money. The alternative is for a person or organization to pay an Internet Service Provider (ISP) to house its content on the Web and make it available through the ISP""s Web server. Of course, most organizations (and people) would like to be perceived as not lacking in either money or expertise. In cyberspace, therefore, an important factor in how an organization is perceived is its Web address. A Web address of XYZCorp.com commands, in a manner of speaking, immediate attention and respect, whereas a Web address of ISP.com/XYZCorp does not, at least to the same extent.
For a person or organization to have the best of both worlds, i.e., house its content on someone else""s server but have it appear to be their own, the server must provide the capability of multi-homing. A multi-homed server behaves as multiple servers in one, responding to requests to multiple addresses, e.g. ISP.com, XYZCorp.com, johnsmith.com, etc. Some existing servers are multi-homed. However, the multi-homing capabilities of existing servers are quite limited. For example, although different customers may have different needs and desire different levels of service, in existing multi-homed servers, as regards a particular physical machine, the core functionality offered by the server (whether extensive or more limited) is necessarily the same for each customer.
An entirely different question concerns the extensibility of Web servers. Because the Web is continually in flux, a Web server must provide a mechanism that allows for extensions to be added to the Web server, or face obsolescence. Presently, the commonly-accepted mechanism for extending the capabilities of existing Web servers is one called the Common Gateway Interface (CGI). The CGI specification has emerged as a standard way to extend the services and capabilities of a Web server having a defined core functionality. CGI xe2x80x9cscriptsxe2x80x9d are used for this purpose. CGI provides an Application Program Interface, supported by CGI-capable Web servers, to which programmers can write to extend the functionality of the server. CGI scripts, however, although they may be compiled, are typically interpreted, meaning that they run at least ten times slower, typically, than compiled binary code. As the complexity of the Web, and hence the amount of time spent by a Web server running CGI scripts, increases, the Web server unavoidably suffers a significant performance hit.
What is needed, then, is a Web server that overcomes the foregoing difficulties.
The present invention, generally speaking, provides a Web server having a multi-homed, modular framework. The modular framework allows extensions to the Web server to be easily compiled into the Web server, allowing the extensions to run natively as part of the server instead of incurring the overhead typical of CGI scripts, for example. The multi-homing capabilities of the Web server provide the appearance to Web users of multiple distinct and independent servers, allowing a small company or individual to create the same kind of Web presence enjoyed by larger companies. In effect, multiple virtual servers run on the same physical machine. The Web server as a whole is easily extensible to allow additional capabilities to be provided natively within the Web server itself. Furthermore, each virtual server is independently configurable in order to turn different capabilities on or off or to modify operation of the virtual server. The Web server is also provided with enhanced security features, built-in animation capability, and other features that afford maximum flexibility and versatility.